Driving Mechanism of a Legged and Wheeled Mobile Robot with Minimal DOFs and Control for Reversible Switching between Walking and Rolling

This paper proposes a design concept for renovating a legged robot to a hybrid mobile robot with minimal degrees of freedom (4DOFs) and its motion analysis for switching locomotion from leg-type to wheel-type and vice versa. For the leg-type locomotion, specifically in the transitional state of sitting or standing, we show the control method based on minimization of total energy cost considering the distribution of a motor power payload in hip and knee joints using a motor specification. Also, we discuss robot configurations for switching between the two types under such environmental factors like walking gaits, ground inclination angle and traveling direction. Knee joint position of a pivotal foot determines knee ahead and knee behind gaits. Then we find three beneficial switching types aiming for moderate use of motor, rider's comfort, and energy saving. Moreover, we clarify the control method for changing traveling direction within a switching period. Finally, we demonstrate the switching and verify that the results of the analysis become useful for enabling the switch on demand. Also, the demonstration verifies that the robot can generate a steering function while it switches between the two types of locomotion.